Inductance coil shielding structure



Jan. l2, 1932. L. L. JNEs INDUCTANCE COIL SHIELDING STRUCTURE 2 Smets-sheet 1 Original Filed June 25, 1926 lNvENToR Leser L.Jorles B Y 2 ATTORNEYS Jan. 12, 1932. L. l.. JoNEs INDUCTANCE COIL SHIELDING STRUCTURE Original Filed June 25, 1926 2 Sheetsf-Sheet 2 INVENTOR Leef L .JONES [s Y A ORNEYS Patented Jan. 12, 1932 UNITED STATES LESTER L. ."IONES, 0F OBADEIL, NEW JERSEY INDU-CTANCE COIL SHIELDING STRUCTURE Application filed June 25, 1926, Serial No. 118,424. Divided and this application led. November 14,

1928. Serial No. 319,336.

This invention relates to an inductance coil and to .an electrostatic shielding means therefor, and has special reference to the provision of radio frequency coils especially suitable for use in the-reception of radiant energy and commonly known as loop antenna coils; and this application is a division of my (zo-pending application Ser. No. 118,424,f`1led June 25, 19:26.

The prime desideratum of my present invention comprehends the provision of radio frequency or loop antenna coils constructed so as to be selfelectrostatically shielded and designed so that the same may be used with highly sensitive radio frequency amplifying systems and arranged in close proximity to the radio amplifier thereof.

A still further prime object of the invention resides in the provision of a supplementary shield for the inductance coil for effecting a more perfect electrostatic shielding thereof.

Radio frequency coils or loop antennae of prior construction and design, such for eX- ample as the known pancake and helical loop structures, are attended in use with wellknown and hitherto insurmountable serious disadvantages. One of the serious objections to these former types of loop antenn is what is known as .antenna eect, this being due to the fact that the loop being commonly connected with one terminal to the grounded filament system andthe other terminal to the high potential or grid electrode of the amplifying tube, tends to act as a vertical antenna owing to the exposure of the high potential wires of t-he loop which normally cover a considerable area. This objectionable antenna effect tends to interfere with the bilateral directivity of the loop and to obscure the sharp minima. Another very serious drawback in these loops of prior design resides in the feed-back reactions which are transferred both magnetically and capacitively from the amplified radio frequency stages to the loop antenna. A loop radio receiving set, in order to be stable and sensitive, mustbe free from these feed-back reactions; and while. the radio frequency stages and the antenna loop may be arranged by known methods to be uncoupled magnetically for all positions of the loop, it has been hitherto found impossible to capacitively decouple the radio frequency coils from the loop except by complete electrostatic shielding of the receiver or the loop.

These objectionable feed-back reactions give rise to other disadvantages, prime among which may be cited the tuning variations of the system as the loop is rotated. The electrosta-tic shielding which has been hitherto necessitated to avoid the feedback reactions, together with the capacity effect of the wooden sides of the radio receiver cabinet, together with the capacity effect of the approaching hand or body of the operator to turn the loop, produce variations in the natural frequency of the loop circuit, which variations undesirably change the tuning characteristics of the system, since the loop circuit is normally very sharply tuned. Such variation-s in the tuning characteristics of the system render it diiiicult to determine the maxima and minima. positions of the loop antenna.

Hy presentinvention has for its principal object the provision of a new radio frequency coil or loop antenna embodying a new meth- 0d of winding the coil whereby the aforementioned disadvantages incident to the use of prior loop structures are effectively obviated, the coil windings being so related that the coil system as a whole is self-capacitively shielded in a manner to overcome the objectionable antenna effect and to minimize the capacitive feed-back reactions between the radio frequency tube and the loop antenna, with the construction moreover such that the loop may be used with highly sensitive radio frequency sets and may be arranged in close proximity to the radio amplifier thereof without necessitating such electrostatic shielding as will produce tuning variations when the loop is rotated. j

Further objects of m present invention include the provision o a coil structure in which the turnsy of the coil are wound so that they are kept tightly stretched in use, producing a mechanically strong loop antenna having a constant inductance; the still further provision of a coil structure of this nature in which the windings are arranged on winding supports so that the forces exerted on the supports by one coil turn operate to increase the tension of and to be balanced by the forces exerted by another turn, producing a mechanically rigid and neat-appearing de si n. y lhe electrostatically shielding inductance coils do not produce a complete elimination of all the external electrostatic fields but rather the substantial elimination or the minimizing thereof to the point where no practical difficulties arise. To more completely eliminate external electrostatic fields, it is a further prime object of my invention to provide a supplementary shielding means which is readily applicable to the loop structure of my invention and which does not appreciably increase the distributed capacity of the winding or the volume swept by the loop as would be the case if similar attempts were made with prior loop structures.

To the accomplishment of the foregoing and such other objects a-s will hereinafter appear, my invention consists in the elements and their relation one to the other as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings, which show the preferred embodiments of my invention, and in which:

Fig. 1 is a perspective view showing a preferred embodiment of the inductance coil embodying the principles of my invention,

Fig. 2 is a cross-sectional View thereof taken in the planes of the broken lines 2 2, Fig. 1,

Fig. 3 is a schematic view considered in cross-section showing the method of winding the coil disclosed in Figs. l and 2,

Fig. 4 is a schematic view showing the winding of a modified form of the coil system of my invention, and

Fig. 5 is a perspective View of the supplemental electrostatic shield showing the principles employed therein.

-Referring now more in detail to the drawings and having reference first to Figs. 1 and 2 thereof, the inductance coil of my present invention comprises a supporting structure or frame F and a coil system generally designated as C. S. composed of windings supported on the frame, said windings comprising inner and outer connected coil sections or layers arranged so that an outer coil section or layer electrostatieally envelops an inner coil section or layer to form an electrostatic shield therefor. In the form of the invention exemplified in the drawings, this multi-layer inductance coil comprises inner, intermediate and outer coil layers, the innermost coil layer being adapted for connection to a point of high potential and the outermost coil layer to a point of low potential. with the arrangement such that each of the coil layers which is exterior to another coil layer is composed of windings which are grouped about the layer within so as-to cnvelop the same whereby each such exteriorly positioned coil layer forms an electrostatic shield for the coil layers within the same.

The arrangement of the coil layers to produce the desired results may be best explained by having reference now to Fig. 3 of the drawings, which figure shows a single series winding composed of 20 turns designated by the reference characters l to 20. The turn or winding l is connected to a point of low potential such as the ground g and the turn or winding 2O is adapted to be connected with a point of high potential such as the grid side of the tuning condenser of the radio receiving set. The windings and turns are, as shown, arranged in alternating relation on opposite sides of and substantially symmetrically with respect to the central plane of the frame F, said central plane being a plane perpendicular to the loop axis a and through the axis of rotation b. With this series winding it will be seen that the turns 19 and 20 comprise the innermost layer adapted for connection to the point of high potential, the turns 15 to 18 comprise a second layer the turns of which are grouped about the innermost layer, the windings 9 to 14 comprising a third layer the turns of which are. grouped about the layers Within the saine, while the turns 1 to 8 comprise a fourth and outermost layer the turns of which are grouped about the layers within th same.

By means of this construction it will be seen that each of the coil layers which is exterior to another coil layer is composed of windings lying in and bounding a surface the axial dimension of which is greater than that of the corresponding surface of the coil layer within the same and that the said windings of such exterior coil layer are grouped about the layer Within so as to envelop the same, whereby each such exteriorly positioned coil layer forms an electrostatic shield for the coil layer or layers within the same. Thus it will be noted that the highest potential turns 19 and 20 are substantially enclosed in the lower potential cage formed by the lower potential wires, the same being true for the succeeding layers which are characterized by progressively lower potential gradients. The turns or windings are arranged to alternate on opposite sides of the coil frame F so as to secure the same average (nearly ground) potential on both sides of the loop to render the residual capacitive coupling substantially invariable as the loop is rotated, such alternation in windings or turns also serving to render the winding operation convenient and facile and producing, moreover, as will be seen hereinafter, a rigid and mechanically strong coil structure.

Referring nowv again to Figs. 1 and 2 of Y' the drawings, the method of winding the multi-layer coil system shown in Fig. 3 will now become more-apparent. In Figs. `1 and 2 the turns or windings are designated with the same reference characters employed 1n Fig. 3 of the drawings. The coil frame F, preferably made of insulating material and which may be made of a good non-conductor such as well dried laminated wood, 1s provided with groups of winding supportsin the form of notched dowel pins p, p' which may also be made of Wood, which supporting ins are driven through holes drilled in the rame and which project through and on opposite sides of the frame F, the p ins being of differing lengthsv :tor permitting the spacing of the turns or windings as desired,

each pin, however, extending preferably on,

opposite sides approximately equal distances from the plane of the frame. `The method of winding the coil system on the frame may be explained by following the winding course from turn 1 to turn 20, althoughv it will be understood that in the actual windin process the structure is begun by first winding turn 20 and ending with turn 1.

The turn or winding 1 which is connected to the frame support 21 is wound about the four pins p at the outermost corners of the frame F, the said turn being then threaded through a slot 22 to the side of the frame F opposite to that on which turn 1 is mounted, the winding being continued as turn 2 on the opposite of said corner pins p, p. After a complete winding of turn 2 is made, the same is re-threaded through the slot 22 and wound about the next group of pins p, p lying in the same horizontal planes with the corner pins p, p. The winding is continued in similar fashion, the wire being threaded through the slot 22 after a turn has been wound so that successive turns of the windings are arranged in alternating relation on opposite sides of and substantially symmetrically with respect to the central plane of the frame, as heretofore stated. 4

By means of this method of winding, it will be seen that an inner or intermediate layer is surrounded substantially on all sides thereof by an outer or exterior layer, the inner layer being elect-rostatically shielded substantially over 360 in each plane. It will also be noted that each dowel pin supports two adjacent Windings, the winding method being such that the forces exerted on a dowel pin by one coil turn operates to increase the tension of and to be balanced by the forces exerted 4by the next adjacent turn on the opposite side of the frame. By means of this construction balanced strains are obtained due to winding and there is no loosening ofv the first windings by distortion of the frame structure due to layer windings such as characterize structures of the prior art. It will be also seen that the pins'arranged in diaprovided with the stub shafts 24 and 25 respectivel The frame may be also cut away at the si es, as clearly shown in Fig. 1 of the drawings, to remove non-essential parts from the internal dielectric field and to make the structure more ornamental. f'

Referring now to the modification shown in Fig. 4 of the drawings, in which similar' parts are designated by reference characters corresponding to those shown with Figs. 1-3, the windings or turns are arranged to secure a lower average potential with respect to the ground of the outer set of wires. To this end the outer layer is Wound with two sets of four turns on opposite sides of the frame and designated 1 to 4 respectively, turns 1 on opposite sides of the frame being connected together to form the ground end of the loop while parallel turns i are connected together to the beginning of turn 5, as clearly shown in Fig 4 oi the drawings. The remaining turns 5 to 16 are wound in alternating relation and in layers similar to that heretofore described. This arrangement gives a considerably lower residual external electrostatic field than that produced by the construction shown in Figs. 1w? of the drawings,

with but slight reduction of the inductance in the loop Moreover, with the construction of Fig. 4 since the outer turns do not cross over through the slot 22 a more perfect elec- .trostatic shield on the slot side of the loop is obtained.

The intensity and direction of the electrostatic ields in the inductance coils embodying the principles of my invention are generally shown in Fig. 3 of` the drawings, and by reference to this figure it will be seen that the turns 19 and 20 of the innermost layer are shielded by the succeeding layers, this being indicated by the electrostatic fields of force shown in dotted lines.

The self-electrostatically shielding inductance coils described do not produce a complete elimination of all the external electrostatic fields, but rather t-he substantial elimination or the minimizing thereof tothe point where no practical diiiiculties arise. To more completely eliminate external electrostatic fields, my invention comprises the addition of a supplementary shielding which is readily applied to the loop structure of my invention and which does not appreciahly increase the distributed capacity of the winding or the volume swept by the loop, as would be the llO case if similar attempts were made with prior i loop structures. This supplementary shielding means is perspectively shown in Fig. 5 of the drawings, the said supplementary shield Y comprising a structure having a configuration such that the same may enclose or surround and be parallel to the loop antenna shown in the preceding figures of the drawings, the loop wires not4 being shown in Fig. 5 to avoid confusion of the disclosure.l

This supplemental shield comprises generically al structure having adjacent open ends and having a ground connection at a point such that the potentials generated at the open ends of the shielding structure due to the E. M. F. induced in the shield by the`inductance coil are equal and in opposite phase. In the construction shown in the drawings this peint of connection is midway between the open ends of the shielding structure. In the form of the invention exemplified the shield comprises lilamentary elements 26, 26, 26 comprising sections of one or more separate wire turns supported'on dowel pins similar to the dowel pin supports for the loop wires hereinhcfore described. Each shield wire 26 or section is broken so as to provide adjacent open ends 2T, 27, which open ends are preferably jointed by an insulating tie such as 28. when a shield of this structure is used in association with the inductanee coil or loop, an E. M. l". is induced in the shield wires which raises the potential in the ends of these wires. Shorting of these ends is impractical because of the induced currents in the loop which would be so formed. To reduce the electrostatic field at a distance due to the induced E. M. F. toa minimum, my invention contemplates the joining of the lilamentary elements or shield turns as hereinabove specilied, which in the form shown in Fig. 5 is at the centers of the lilamentary elements for purposes of grounding, this be` ing shown by the junction line 29 connecting the shield filaments at points midway between the open ends thereof', the said junction line being connected to the ground The junction point of the shield should be near the place where the loop ends lead olf to the tuning condenser, and the ground connectiou provided should preferably be made to or through the same wire that connects the grounded plate system of the tuning condenser. I have found that this system of grounding is essential where it is desired to have the lowest possible electric field at a distance. This method of ground connection reduces the induced E. M. F. to a minimum and raises the adjacent ends of the filaments to opposite potentials with respect to ground, the result being that at a small distance the potential due to one end of the shield neutralizes that due to the other end of the shield and thus substantially eliminates the electrostatic residual. The effect produced will be better understood when it is seen that the shield turns are threaded by substantially the entire magnetic flux passing through the loop and therefore has induced in each of its turns the same voltage as is induced in each of the outer turns of the loop antenna structure. If, then, for example, the center or mid-point of a single turn section begrounded, then there will exist equal and op osite potentials with respect to ground on tlie o en ends of such turn, which otentials will e approximately one-half t e difference of potential across the adjacent outer turns of the loop.

While I prefer to make the ground junction point mid-way between the open ends of the filament-ary shielding elements, it will be readily seen that the junction point may `be placed at other points of the filamentary elements so long as the resultant effect is to produce the equal and opposite potentials at the' open ends of the filaments. Thus the same results may be secured by joining the filamentary elements at one of their ends and running the grounding wire back along the surface of the shielding wires to the bottom mid-point thereof and then away from the loop to the ground. The equivalency of this structure will be seen when it is realized that the potentials produced in the half turn grounding wire are equal to that in the half turns ot' the shield near which this grounding wire is run, so that the resulting effect is that equal and opposite potentials are generated in the adjacent open ends of the shielding structure. 4

The manner of making and using my improved inductance coil and shield therefor and the many advantages incident thereto will in the main be fully apparent from the above detailed description thereof. It will be manifest that besides producing an electrostatically shielded antenna coil which eliminates the disadvantageous antenna effeet, feed-back reactions and tuning variations characterized by structures of the prior art, I have produced a construction which is subject to ease of winding and economical manufacture embodying' low dielectric losses and a maximum leakage path between the turns of the coil system. It will be also manifest that the structure provided is rigid, the windings producing balanced strains on the winding supports resulting in effecting an inductance coil system in which the inductance i may be maintained constant in use and ell'ecting an inductance coil which presents a neat appearance.

`While I have shown my invention in the preferred forms, it will be apparent that many changes and modifications may be made in the structure disclosed without departing from the spirit of the invention, defined in the following claims.

I claim:

l. The combinationv with a loop antenna, of an electrostatic shield comprising a loop enclosing structure extending` entirely around the periphery of the loop in coaxial relation therewith, said structure having adjacent idpen ends and having a ground connection ments extending entirely around the periphery of the coil in coaxial relation therewlth, the said elements having open ends and having a ground connecten midway between the said open ends.

3. An electrostatic shield for an inductance coil comprising wire turns adapted to enclose the inductance coil, each turn having open ends joined by an insulating tie, .the said turns being joined together at points midway between the open ends thereof to form a ground connecting junction.

4. In combination with an inductance coil, of an electrostatic shield comprising a coil enclosing structure having open ends and means for grounding said shield structure at a region therein such that the potentials generated at the open ends of the shielding structure due to the voltage induced therein by the inductance coil are in opposite phase.

5. In combination with an inductance coil, oi an electrostatic shield comprising c oil enclosing iilamentary elements, the said elements having open ends, the said filamentary elements being joined together 1n a region for connection to ground such that the potentials generated at the open ends of the ila-mentary elements due to the voltage induced therein by the inductance coil are in opposite phase.

6. ln combination, a multi-layer inductance coil comprising inner and outer connected coil sections, the inner coil section being adapted for connection to a point of high potential and the outer coil section to a point of lovs7 potential, the outer coil section comprising a winding layer lying in and bounding a surface the axial dimension of which is greater than that of the corresponding inner coil section surface and the said windings of the outer coil section being grouped about the inner coil section so as to envelop the same whereby the outer coil section forms an electrostatic shield for the inner coil section, and an electrostatic shield for said inductance coil comprising a coil enclosing structure having open ends and means for grounding said shield structure at a region therein such that the potentials generated at the open ends of the shield structure due to the voltage induced therein by the inductance coil are in opposite phase.

7. In combination, a multi-layer inductance coil comprising a series of connected coil sections forming inner, intermediate and outer coil layers, the innermostcoil layer being adapted for connection to a point of high potential and the outermost coil layer to a point of low potential, each of the coil layers exterior to another coil layer comprising windings lying in and bounding a surface the axial dimension of which is greater than that of the corresponding surface of the coil lafyer within the same, and the said windings o such exterior coil layer being grouped about the layer within so as to envelo the same whereby each such exteriorly positloned coil'layer forms an electrostatic shield for the coil layers within the same, and an electrostatic shield for said inductance coil comprising a coil enclosing structure having open ends and means for grounding said shield structure at a region therein such that the potentials generated at the open ends of the shielding structure due to the voltage induced therein by the inductance coil are equal and in opposite phase.

8. In combination, a multi-layer inductance coil comprising a coil frame and a plurality of winding layers thereon, the windings of the layers being arranged in alternating relation on opposite sides of the plane of said frame, said windings forming two multi-layer groups, one multi-layer group lying wholly on one side and the other multilayer group lying` wholly on the other side of said plane; and an electrostatic shield for said inductance coil comprising al coil enclosing structure having open ends .and means for grounding said shield 'structure at a region therein such -that the potentials generated at the open ends of the shielding structure due to the voltage induced therein by the inductance coil are in opposite phase.

9. In combination, a. multi-layer inductance coil comprising a coil frame and windings thereon, successive turns of the windings being arranged in alternating relation on opposite sides of a central plane of said frame, said alternating turns forming two multilayer groups, one multi-layer group lying Wholly on one side and the other multi-layer group lying Wholly on the other side of said plane, and both multi-layer groups being arranged substantially symmetrically With respect to the central plane of said frame; and an electrostatic shield for said inductance coil comprising a coil enclosing structure having open ends and means for grounding said shield structure at a region therein such that the potentials generated at the open ends of the shielding structure due to the voltage induced therein by the inductance coil are in orly positioned coil layer forms an electrostatic shield for the coil layers within the same; and an electrostatic shield for said inductance coil comprising coil enclosing filalnentary elements, the said elements having open ends, the said filamentary elements being joined together in a region for connection to ground such that the potentials generated at the o en ends of the lilamentary elements due to t e voltage induced therein by the inductance coil are in opposite phase.

11. An electrostatic shield for a loop antenna coil comprising wire turns arranged coaxially with the antenna turns and adapted to entirely enclose the antenna coil, each of said turns having open ends in order to open circuit the same.

12. In combination with a loop antenna coil, an electrostatic shield comprising a coil enclosing structure comprising Wire turns having open ends and means for grounding the turns of said shield structure and the outer turn of said antenna coil.

Signedat New York in the county of New7 York and State of New York this 10th day of November, A. D. 1928. v

LESTER L. JONES. 

